Mineralogy, Geochemistry and Genesis of the Bagoushi Karst Bauxite Deposit, Northwestern Fars Province, Iran

Bagoushi deposit is located in 37 km northwestern Masiri in Fars province. Structurally the deposit is situated in the Zagros Simply Folded Mountain belt and developed in Upper Cretaceous carbonates. From the top to bottom, the deposit is consisting of red, pisolitic, brown, brecciate, and kaolinitic bauxite horizons. Boehmite, kaolinite, hematite, pyrophyllite, anatase, calcite and diaspore are the major mineral phases. The main ore textures of the deposit include pisolitic, pisolitic-oolitic and clastic with pelitomorphic and microgranular matrixes. According to the formation conditions of the major minerals, the Bagoushi deposit formed in an environment ranging from acidic-oxidizing surface water to basic and reducing groundwater. Some textural features such as pelitomorphic matrix, pisolitic and oolitic textures, radial fractures in pisoids, growth of simple cortex around earlier pisoids, pisoids with cortexes lacking radial and circular fractures, are indicative of allochthonous origin; and broken pisoids, allogeneic pisoids and clastic grains reveal the transportation of bauxitic materials; therefore the bauxite materials is authigenic, but in some parts were transported and re-deposited, at least locally. The mass change calculations relative to the immobile element Ti show that elements such as Si, Fe, Mg, K and Na are leached out; Al, Zr, V, Th, Nb, Ba and REEs particularly LREE are concentrated; and Hf, Ta, Co, Rb, Cs, Be and U are relatively immobile during the bauxitisation process. The bauxite ores are characterized by progressive enrichment of the REE compared to parent rock, intense LREE/HREE fractionation, relatively stable negative Eu anomalies, and weak negative Ce anomalies.